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Clinical Calculations: Module 6: Divided Doses and Reconstituted Medications

Divided Doses and Reconstituted Medications

Module 6 – Calculating Divided Doses and Doses of Reconstituted Medications

What’s in this module?

There are two problem types in this module: medication given in divided doses and reconstitution of powdered medications.

Summary of problem types in this module

Problems will involve reading medication labels and healthcare provider’s orders.  You will calculate the correct amount to give a client of oral, injectable, and intravenous medications.  Assume all questions ask for the amount per dose unless instructed otherwise.

Equivalents to know

You should now know all your commonly used equivalents.

Rounding rules to know

You will continue to use the rounding rules for numbers >1 and <1.

You will also need to refer to your rounding rules for tablets and capsules.

Starting factors and answer units

The SF in most of the problems is the amount of medication the healthcare provider has prescribed.  The dose is usually stated in mg, mcg, or g. 

Weight-based medications will use the client’s weight as the SF. 

Medication Given in Divided Doses

The healthcare provider may prescribe the total amount of a medication to be given in a day (24 hours).  The medication prescription may state that the medication is to be given in a specific number of doses (for example, four times daily).  The medication prescription may state that the medication is to be given after a certain amount of time has passed (for example, every 6 hours).  Note that the two intervals stated as examples are really the same.  Every 6 hours is the same as 4 times daily.

The nurse will calculate the amount to give for the entire day then divide the ordered number of dose.  Note: do not round the quantity of medication until the amount per dose is calculated.  Rounding before the amount per dose is calculated may result in an incorrect quantity per dose and in total.

If the problem does not state divided doses, the prescription is written for one dose.

Problem Type 1 – Medication Given in Divided Doses

Image is a label from a vial of Ativan. The label states "Ativan Injection, (lorazepam injection, U.S.P.)", 4 milligrams per milliliter.

https://www.drugs.com/pro/images/5fc0e987-61c9-40c4-b0d5-fcea07c8733e/ativan-injection-7.jpg     Retrieved 2/5/19

Example 1:

A healthcare provider has prescribed lorazepam 4 mg IM in six divided doses.  How much will the nurse give per dose?

Here’s the problem set up in the dimensional analysis format:

SF = 4 mg

AU = ml per dose

Equivalents:

4 mg = 1 ml  (see the drug label)

Equation for the dose in ml:

The equation is 4 milligrams over 1 times 1 milliliter over 4 milligrams. Cross out milligrams. That leaves milliliter which is your answer unit. Solve the equation to get an answer of 1 ml for the daily dose, to be divided by 6 doses to determine how many milliliters to give per dose. One milliliter divided by 6 doses equals 0.166, which rounds to 0.17 milliliters per dose.

 

Image of a label from a 50 milliliter bottle of Zofran (registered trademark oral solution). The label also has the name ondansetron hydrochloride, 4 milligrams per 5 milliliters.

https://www.drugs.com/pro/images/c7d61d98-fe86-4340-9b86-47eb92acaa0e/zofran-oral-spl-graphic-07.jpg   Retrieved 2/5/19

Example 2:

A healthcare provider has prescribed ondansetron HCl 24 mg orally daily in divided doses every 8 hours.  How many ml will the nurse give per dose?

SF = 24 mg

AU = ml per dose

Equivalents:

4 mg = 5 ml (see label)

Equation for the dose in ml:

The equation is 24 milligrams over 1 times 5 milliliters over 4 milligram. Cancel milligrams. That leaves milliliters which is your answer unit. Solve the problem to get 120 over 4 which reduces to an answer of 30 milliliters. That is the daily dose. The medication is prescribed every 8 hours, or three times a day. To determine the number of milliliters to give per dose, divide 30 milliliters by 3 doses to get the final answer of 10 milliliters per dose.

 

Reconstitution of Powdered Medications

Some medication is supplied in a powdered form and must mixed with a specified liquid (diluent) before it is used. 

 

Image contains definitions for 5 key terms. (1) Concentration: How much solute is dissolved in a certain amount of fluid. This is going to be a specific amount of drug which is dissolved in a specific amount of fluid. (2) Diluent: Product added to a solution, powder, ointment, cream, or other product used to reconstitute, dissolve, or dilute another product. (3) Medication Reconstitution: Using the given directions, or recipe, on a prescription label to reconstitute the powder contained inside to a specific concentration as indicated. (4) Reconstitution: The process of adding a diluent to a dry ingredient to make it a liquid. (5) Shelf life: The length of time medication can be stored safely and administered.

http://www.austincc.edu/rxsucces/pdf/reconstructionpdf.pdf     Retrieved 1/27/19

 

Image illustrating how to reconstitute a medication. There is a label indicating that you have a vial of 500 milligrams of oxacillin sodium in dry powder form. The instructions indicate to add 2.7 milliliters of sterile water for injection. and that each 1.5 milliliters of solution will then contain 250 milligrams of medication. The steps involved include (1) holding the vial of sterile water for injection upright and adding 2.7 milliliters of air with a syringe and needle. (2) Turning the vial upside down and withdrawing 2.7 milliliters of sterile water with the syringe and needle. (3) Injecting the vial of powder with the 2.7 milliliters of sterile water. (4) a image of the now liquid form of oxacillin labeled 500 milligram per 3 milliliters (which is the same concentration as 250 milligrams per 1.5 milliliters that was indicated on the label).

https://basicmedicalkey.com/wp-content/uploads/2017/02/B9780323056298500313_gr1.jpg  Retrieved 1/27/19

 

Instructions for reconstitution will be provided on the drug label or package insert.  Be certain that you are using the correct diluent in the correct quantity for each medication,

In the label above, 2.7 ml of sterile water is the specified diluent for oxacillin sodium.  First inject 2.7 ml of air into the vial of sterile water to compensate for the volume of fluid to be removed.  Then withdraw 2.7 ml of sterile water to use as the diluent. 

Inject the sterile water into the vial of powdered medication.  Swirl or rotate to mix as directed.  The medication is then ready to use.  The date and time of reconstitution and the nurse’s name must be recorded on the vial of medication because medication must not be used after its shelf life has expired.

The dosage strength of the reconstituted medication will be specified on the label.  The dosage strength of the reconstituted medication is the strength the nurse will use in calculating the amount of medication to give the client according to the healthcare provider’s prescription.

 

Image of a label from a vial of Pfizerpen (penicillin G potassium) powder. The instructions for reconstitution has three parts. (1) If you add 75 milliliters of diluent to the powder, the concentration will be 250,000 units per milliliter. If you add 35 milliliters of diluent to the powder the concentration will be 500,000 units per milliliter. (3) If you add 11.5 milliliters of diuent to the powder, the concentration will be 1,000,000 units per milliliter.

https://basicmedicalkey.com/wp-content/uploads/2017/02/B9780323056298500313_fx19.jpg   Retrieved 1/27/19

 

Some medications will give a range of diluent amounts, each resulting in a different dosage strength of the medication.  See the right side of the medication label above. The amount of diluent to use will be selected based on the dose to be given.  The amount of diluent used must be recorded so the dosage strength will be clear to anyone using the reconstituted medication.

Recording the amount of diluent used will prevent possible medication errors due to a misunderstanding of the medication dosage strength.

Problem Type 2 – Reconstitution of Powdered Medications

Image of a label from a bottle of Fluconazole dry powder for oral suspension. Mixing Instructions indicate to tap bottle lightly to loosen powder. Add 24 milliliters of distilled water or Purified Water to the bottle and shake well. The label indicates that there will be 35 milliliters in the bottle when it is reconstituted and there will be 40 milligrams per milliliter. There is an additional notation that each teaspoon (5 milliliters) contains 200 milligram fluconazole when reconstituted.

https://www.drugs.com/pro/images/bf92a7d7-395b-4e2c-a3c4-66ebdbfd1052/fpl-bl-40mgperml-35ml-06.jpg   Retrieved 1/27/19

 

Example 1:

The healthcare provider has prescribed fluconazole oral suspension 200 mg by mouth  daily for 7 days.  How many ml will the nurse give to the client per dose?

SF = 200 mg

AU = ml

Equivalents:

Note - The nurse has added 24 ml of distilled or purified water to the powdered medication for reconstitution, but this amount is not relevant in calculating the dose to give.  The label states the drug strength after reconstitution.

40 mg = 1 ml

Equation for the dose in ml:

The equation is 200 milligrams over 1 times 1 milliliter over 40 milligrams. Cancel milligrams. That leaves milliliter which is your answer unit. Solve the equation to get 200 milliliters over 40 which reduces to the final answer of 5 milliliters.

 

Image from a 1 gram vial of Streptomycin in dry powder form. The label indicates 3 possible reconstitution recipes. If 4.2 milliliters of sterile water are added, the concentration will be 200 milligrams per milliliters. If 3.2 milliliters of sterile water are added, the concentration will be 250 milligrams per milliliter. If 1.8 milliliters of sterile water are added, the concentration will be 400 milligrams per milliliter.

https://www.drugs.com/pro/images/abd1f64e-4283-4370-aae8-3666316aa36e/streptomycin-for-injection-usp-2.jpg  Retrieved 1/27/19

Example 2:

The healthcare provider has prescribed 2 g streptomycin IM daily divided every 8 hours for your client.  Your charge nurse recommends that you use 1.8 ml of sterile water to reconstitute the medication to reduce the volume to be injected.  How many ml will you give per dose?

SF = 2 g

AU = ml per dose

Equivalents:

1 g = 1000 mg

400 mg = 1 ml  (from the reconstitution directions on the label)

You do not use the 1.8 ml of diluent added in your calculations, but you need this information to find the 400 mg per ml after reconstitution from the drug label. 

Equation for the dose in ml:

The equation is 2 grams over 1 times 1000 milligrams over 1 gram times 1 milliliter over 400 milligrams. Cancel gram and milligram. That leaves milliliter which is your answer unit. Solve the equation to get 2000 milliliters over 400 which reduces to 5 milliliters to be given daily. To determine the number of milliliters per dose, divide the 5 milliliters by 3 doses to get 1.67 which rounds to 1.7 milliliters per dose.

Please notice:

One day = 24 hours

Every 8 hours  =  3 doses per day

 

 

Practice Problems

Module 6 Practice Problems

 

Image of label for Adderall XR. Each capsule contains 15 milligrams of medication.

https://www.drugs.com/pro/images/aff45863-ffe1-4d4f-8acf-c7081512a6c0/adderall-xr-4.jpg   Retrieved 2/5/2019

Use the Adderall XR label above for problems 1 and 2.

  1.  You are working with a young adult client.  The healthcare provider has prescribed Adderall XR capsules 60 mg daily in two divided doses at 0600 and 1200.  How many capsules will the client take per dose? 

  1. Your client taking Adderall XR has a new prescription.  The client will now take the 45 mg of the medication daily in three divided doses at 0600, 1100, and 1400.   How many capsules will the client take per dose? 

 

Image of label from Benedryl (diphenhydramine) elixir. Each 5 milliliters contains 12.5 milligrams of diphenhydramine.

https://basicmedicalkey.com/wp-content/uploads/2016/06/B9781437723663000102_b010-004-9781437723663.jpg   Retrieved 2/5/2019

Use the Benadryl label above for problems 3 and 4.

  1. A nurse is working in a pediatric clinic.  A client who is 11 years old has a new prescription for diphenhydramine HCl elixir 40 mg by mouth daily in four divided doses.  How many mL will the client take per dose?

  1. The prescription for the 11-year-old client in problem 3 has changed.  The client will now take diphenhydramine HCl elixir 60 mg by mouth daily in four divided doses.  How many mL will the client take per dose?

 

Image of label for Dilantin oral suspension. The label indicates that the strength of the medication is 125 milligrams per 5 milliliters.

https://www.drugs.com/pro/images/051742b5-b0f0-44a5-8d31-3288527b0638/dilantin-04.jpg  Retrieved 2/5/2019

Use the label for Dilantin-125 above for problems 5 and 6.

  1. A nurse is working with a 16-year-old client.  The healthcare provider has written a prescription for phenytoin oral suspension 7 mg/kg/day by mouth in three divided doses.  The client weighs 125 pounds.  How many mL will the client take per dose?

  1.  The nurse has another client who is 12 years old.  This client has a prescription for phenytoin oral suspension 6 mg/kg/day by mouth in three divided doses.  The client weighs 55 kg.  How many mL will the client take per dose?

 

Image of label for ondansetron. The label states that the strength of the medication is 4 milligrams per 2 milliliters.

http://drugsdb.eu/images/ondansetron_hydrochloride_Ondansetron-injection-2ml-label.jpg   Retrieved 2/5/2019

Use the label for ondansetron injection above for problem 7.

  1. A nurse working on a hospital medical client has a client on IV fluids.  The healthcare provider has written an additional order for ondansetron 24 mg IV in three divided doses.  How many mL of ondansetron will the nurse give per dose?

 

Image of label from Tobramycin injection. The label indicates that the strength of the medication is 80 milligrams per 2 milliliters.

https://medlibrary.org/lib/images-rx/tobramycin-sulfate-2/80cdc563-140a-404f-bbcd-eaef1684b705-04.jpg   Retrieved 2/5/2019

Use the tobramycin label above for problem 8.

  1. The hospitalized client from problem 7 above has a new prescription for tobramycin 1.5 mg/kg/day IV every eight hours in divided doses.  The client weighs 180 pounds.  How many mL will the nurse give per dose?

 

Image of label from Phenergan Injection. The label indicates that the strength of the medication in 25 milligrams per milliliter.

https://medlibrary.org/lib/images-rx/phenergan/7f845a30-d055-452d-957f-a8be87f52815-03.jpg   Retrieved 2/5/2019

Use the Phenergan injection label above for problems 9 and 10.

  1. Your adult client has a prescription for promethazine HCl injection IM 100 mg daily in three divided doses.  How many mL will you give per dose?

  1. Your client’s prescription has changed to promethazine HCl injection IM 80 mg daily in three divided doses.  How many mL will you give per dose?

 

Image of label for Amoxicillin. Directions for mixing: Tap bottle until all powder flows freely. Add approximately 1/3 total amount of water for reconstitution (total equals 59 milliliters); shake vigorously to wet powder. Add remaining water; again shake vigorously. Each 5 milliliters (1 teaspoonful) will contain amoxicillin trihydrate equivalent to 250 milligrams of amoxicillin.

https://www.rxresource.org/image.php?src=75ca51d0-343c-48c2-9873-2a3c45e8ffe8/250mg-80ml-label.jpg   Retrieved 2/5/2019

Use the label above for amoxicillin oral suspension for problems 11 and 12.

  1.  Your adult client has a prescription for amoxicillin oral suspension 1300 mg by mouth daily in three divided doses.  What diluent will you mix with the powder for reconstitution?  How much diluent will you use?  How many mL of the reconstituted medication will you give per dose?

  1. Another of your adult clients has a prescription for amoxicillin oral suspension 400 mg by mouth every eight hours.   How many mL of the reconstituted medication will you give per dose?

 

Image of label for Zithromax. The label states to constitute to 100 milligrams per milliliter with 4.8 milliliters of sterile water for injection.

https://aidsinfo.nih.gov/images/xml-images/0069-3150-83/zithromax-iv-03.jpg  Retrieved 2/5/2019

Use the Zithromax label above for problems 13 and 14.

  1.    Your hospitalized adult client has a prescription for azithromycin 500 mg IV daily for two days.  How many mL will you give per dose?

  1.  Your client’s prescription has changed to azithromycin 450 mg IV daily.  How many mL will you give per dose?

 

Image of label for Ryanodex (dantrolene sodium). Directions state that each single-dose vial contains 250 milligrams of dantrolene sodium when reconstituted with 5 milliliters of sterile water for injection.

https://www.drugs.com/pro/images/8f7b3ac0-604d-4c78-b545-5e0f8ea3d698/dan00-0001-03.jpg   Retrieved 1/27/19

Use the label for Ryanodex for questions 15 and 16.

  1. A nurse is caring for a hospitalized adult client who weighs 150 pounds.  The healthcare provider has written a prescription for dantrolene sodium IV 1 mg/kg every four hours.  How many mL will the nurse give per dose?  What is the diluent used to reconstitute the medication?

  1. The client in question 15 has a new prescription.  The prescription for dantrolene sodium IV has changed to 2.5 mg/kg IV every six hours.  How many mL will the nurse give per dose?

 

Image of label for Pfizerpen. The directions include instructions for three concentrations: (1) Add 75 milliliters of sterile water for injection to yield a concentration of 250,000 units per milliliter, (2) add 33 milliliters of sterile water for injection to yield 500,000 units per milliliter, and (3) add 11.5 milliliters of sterile water for injection to yield 1,000,000 units per milliliter.

https://clinicalgate.com/wp-content/uploads/2015/03/B9781437723663000114_b011-013-9781437723663.jpg    Retrieved 1/27/19

Use the Pfizerpen label above for questions 17 through 20.

A nurse is working on a hospital medical unit and has several clients with prescriptions for penicillin G potassium IV.

  1.  Client A has a prescription for 10 million units of penicillin G potassium IV daily in four divided doses.  The bottle of penicillin G potassium available on the unit was reconstituted using 75 mL of sterile water.  How many mL will the nurse give per dose?

  1.   Client B has a prescription for 20 million units of penicillin G potassium IV daily in six divided doses.  The nurse uses 33 mL of sterile water to reconstitute a new bottle of  penicillin G potassium.   How many mL will the nurse give per dose?

  1.   Client C has a prescription for 30 million units of penicillin G potassium IV daily in six divided doses.  The nurse uses 75 mL of sterile water to reconstitute a new bottle of  penicillin G potassium.   How many mL will the nurse give per dose?

  1. The prescription for client C has changed to 25 million units of penicillin G potassium IV daily in four divided doses.  The nurse still has medication in the bottle of penicillin G potassium reconstituted with 75 mL of sterile water.  How many mL will the nurse give per dose?

 

Answers to Practice Problems

Module 6 Answers to Practice Problems

Why do you often need the client’s age?  Doses of the medication often differ by age, especially when the clients are children or teens.

 

The Adderall XR questions:

  1. You are working with a young adult client.  The healthcare provider has prescribed Adderall XR capsules 60 mg daily in two divided doses at 0600 and 1200.  How many capsules will the client take per dose? 

SF = 60 mg

AU = capsules

Equivalents:

1 capsule = 15 mg

2 doses

Equation for the dose in caps:

The equation is 60 milligrams over 1 times 1 capsule over 15 milligrams. Cancel milligrams. That leaves capsule which is the answer unit. Solve the equation to get 4 capsules. Divide by the two doses to get the answer of 2 capsules per dose.    

 

  1. Your client taking Adderall XR has a new prescription.  The client will now take the 45 mg of the medication daily in three divided doses at 0600, 1100, and 1400.   How many capsules will the client take per dose?

SF = 45 mg

AU = capsules

Equivalents:

1 capsule = 15 mg

3 doses

Equation for the dose in caps:

 The equation is 45 milligrams over 1 times 1 capsule over 15 milligrams. Cancel milligrams. That leaves capsule which is the answer unit. Solve the equation to get 3 capsules. Divide by the 3 doses to get the final answer of 1 capsule per dose.

  

The Benadryl questions:

  1. A nurse is working in a pediatric clinic.  A client who is 11 years old has a new prescription for diphenhydramine HCl elixir 40 mg by mouth daily in four divided doses.  How many mL will the client take per dose?

SF = 40 mg

AU = mL

Equivalents:

5 mL = 12.5 mg

4 doses

Equation for the dose in mL:

The equation is 40 milligrams over 1 times 5 milliliters over 12.5 milligrams. Cancel milligrams. That leaves milliliters which is the answer unit. Solve the equation to get 16 milliliters. Divide by the four doses to get a final answer of 4 milliliters per dose.

 

  1. The prescription for the 11-year-old client in problem 3 has changed.  The client will now take diphenhydramine HCl elixir 60 mg by mouth daily in four divided doses.  How many mL will the client take per dose?

SF = 60 mg

AU = mL

Equivalents:

5 mL = 12.5 mg

4 doses

Equation for the dose in mL

The equation is 60 milligrams over 1 times 5 milliliters over 12.5 milligrams. Cancel milligrams. That leaves milliliters which is the answer unit. Solve the equation to get 24 milliliters. Divide by the 4 doses to get a final answer of 6 milliliters per dose.

 

The Dilantin questions:                

  1. A nurse is working with a 16-year-old client.  The healthcare provider has written a prescription for phenytoin oral suspension 7 mg/kg/day by mouth in three divided doses.  The client weighs 125 pounds.  How many ml will the client take per dose?

Remember: In weight-based problems, the client’s weight is the starting factor.  If the weight is in pounds and the prescription is in kg, a weight conversion should be built into your equation.

SF = 125 lbs

AU = mL

Equivalents:

5 mL = 125 mg

1 kg = 2.2 lbs

3 doses

Equation for the dose in mL:

The equation is 125 pounds over 1 times 1 kilogram over 2.2 pounds times 7 milligrams over 1 kilogram times 5 milliliters over 125 milligrams. Cancel like units. That leaves milliliters which is the answer units. Solve the equation to get 15.909 milliliters. Do not round at this point. Divide by the 3 doses to get a final answer of 5.3 milliliters.

In this problem there is no difference in the answer, but remember to not round your answer to the appropriate number of decimal places until you reach your final answer.

 

  1. The nurse has another client who is 12 years old.  This client has a prescription for phenytoin oral suspension 6 mg/kg/day by mouth in three divided doses.   The client weighs 55 kg.  How many mL will the client take per dose?

SF = 55 kg

AU = mL

Equivalents:

5 mL = 125 mg

3 doses

Equation for the dose in mL:

The equation is 55 kilograms over 1 times 6 milligrams over 1 kilogram times 5 milliliters over 125 milligrams. Cancel like units. That leaves milliliters which is the answer unit. Solve the equation to get 13.2 milliliters. Divide by the 3 doses to get a final answer of 4.4 milliliters per dose.

 

The Ondansetron question:

  1. A nurse working on a hospital medical client has a client on IV fluids.  The healthcare provider has written an additional order for ondansetron 24 mg IV in three divided doses.  How many mL of ondansetron will the nurse give per dose?

SF = 24 mg

AU = mL

Equivalents:

1 mL = 2 mg

3 doses

Equation for the dose in mL:

The equation is 24 milligrams over 1 times 1 milliliters over 2 milligrams. Cancel like units. That leaves milliliters which is the answer unit. Solve the equation to get 12 milliliters. Divide by the 3 doses to get a final answer of 4 milliliters per dose.   

 

The Tobramycin question:

  1. The hospitalized client from problem 7 above has a new prescription for tobramycin 1.5 mg/kg/day IV every eight hours in divided doses.  The client weighs 180 pounds.  How many mL will the nurse give per dose?

SF = 180 lbs

AU = mL

Equivalents:

1 mL = 40 mg

1 kg = 2.2 lbs

3 doses

Equation for the dose in mL:

The equation is 180 pounds over 1 times 1 kilogram over 2.2 pounds times 15 milligrams over 1 kilogram times 1 milliliter over 40 milligrams. Cancel like units. That leaves milliliters which is the answer unit. Solve the equation to get 3.068 milliliters. Do not round at this point. Divide by the 3 doses to get 1.02 which rounds to 1 milliliter per dose.

 

The Phenergan questions:

  1. Your adult client has a prescription for promethazine HCl injection IM 100 mg daily in three divided doses.  How many mL will you give per dose?

SF = 100 mg

AU = ml

Equivalents:

1 mL = 25 mg

3 doses

Equation for the dose in mL:

The equation is 100 milligrams over 1 times 1 milliliter over 25 milligrams. Cancel milligrams. That leaves milliliters which is the answer unit. Solve the equation to get 4 milliliters. Divide by the 3 doses to get 1.33 which rounds to 1.3 milliliters per dose.

 

  1.  Your client’s prescription has changed to promethazine HCl injection IM 80 mg daily in three divided doses.  How many mL will you give per dose?

SF = 80 mg

AU = mL

Equivalents:

1 mL = 25 mg

3 doses

Equation for the dose in mL:

The equation is 80 milligrams over 1 times 1 milliliter over 25 milligrams. Cancel milligrams. That leaves milliliters which is the answer unit. Solve the equation to get 3.2 milliliters. Divide by the 3 doses to get a final answer of 1.06 which rounds to 1.1 mL per dose.

 

The Amoxicillin questions:

  1. Your adult client has a prescription for amoxicillin oral suspension 1300 mg by mouth daily in three divided doses.  What diluent will you mix with the powder for reconstitution?  How much diluent will you use?  How many mL of the reconstituted medication will you give per dose?

The diluent is water. You are to add 59 mL of water to the powder.

SF = 1300 mg

AU = mL

Equivalents:

5 mL = 250 mg

3 doses

Equation for dose in mL:

The equation is 1300 milligrams over 1 times 5 milliliters over 250 milligrams. Cancel milligrams. That leaves milliliters which is the answer unit. Solve the equation to get 26 milliliters. Divide by the 3 doses to get a final answer of 8.66 which rounds to 8.7 milliliters per dose.

     

  1.  Another of your adult clients has a prescription for amoxicillin oral suspension 400 mg by mouth every eight hours.   How many mL of the reconstituted medication will you give per dose?

SF = 400 mg

AU = mL

Equivalents:

5 mL = 250 mg

Equation for dose in mL:

The equation is 400 milligrams over 1 times 5 milliliters over 250 milligrams. Cancel milligrams. That leaves milliliters which is the answer unit. Solve the equation to get 8 milliliters per dose.

This problem is not written for divided doses.  The dose stated will be given every 8 hours.

 

The Zithromax questions:

  1. Your hospitalized adult client has a prescription for azithromycin 500 mg IV daily for two days.  How many mL will you give per dose?

SF = 500 mg

AU = mL

Equivalents:

1 mL = 100 mg

Equation:

The equation is 500 milligrams over 1 times 1 milliliter over 100 milligrams. Cancel milligrams. That leaves milliliters which is the answer unit. Solve the equation to get 5 milliliters per dose.

This problem is not written for divided doses.  The dose stated will be given every day.

The medication label states to dilute further before use.  That would be done after the correct dose is drawn from the vial.

 

  1. Your client’s prescription has changed to azithromycin 450 mg IV daily.  How many mL will you give per dose?

SF = 450 mg

AU = mL

Equivalents:

1 mL = 100 mg

Equation:

The equation is 450 milligrams over 1 times 1 milliliter over 100 milligrams. Cancel milligram. That leaves milliliter which is the answer unit. Solve the equation to get 4.5 milliliters per dose.

This problem is not written for divided doses.  The dose stated will be given every day.

The medication label states to dilute further before use.  That would be done after the correct dose is drawn from the vial.

 

The Ryanodex questions:

  1. A nurse is caring for a hospitalized adult client who weighs 150 pounds.  The healthcare provider has written a prescription for dantrolene sodium IV 1 mg/kg every four hours.  How many mL will the nurse give per dose?  What is the diluent used to reconstitute the medication?

SF = 150 lbs

AU = mL per dose

Equivalents:

1 mL = 50 mg

1 kg = 2.2 lbs

Equation:

The equation is 150 pounds over 1 times 1 kilogram over 2.2 pounds times 1 milligram over 1 kilogram times 1 milliliter over 50 milligrams. Cancel like units. That leaves milliliters which is the answer unit. Solve the equation to get 1.36 which rounds to 1.4 milliliters per dose.

This problem is not written for divided doses.

The diluent is sterile water for injection (supplied in a vial).

 

  1. The client in question 15 has a new prescription.  The prescription for dantrolene sodium IV has changed to 2.5 mg/kg IV every six hours.  How many mL will the nurse give per dose?

SF = 150 lbs

AU = mL per dose

Equivalents:

1 mL = 50 mg

1 kg = 2.2 lbs

Equation:

The equation is 150 pounds over 1 times 1 kilogram over 2.2. pounds times 2.5 milligrams over 1 kilogram times 1 milliliter over 50 milligrams. Cancel like units. That leaves milliliters which is the answer unit. Solve the equation to get 3.40 which rounds to 3.4 milliliters per dose.

This problem is not written for divided doses.

 

The Pfizerpen questions:

  1. Client A has a prescription for 10 million units of penicillin G potassium IV daily in four divided doses.  The bottle of penicillin G potassium  available on the unit was reconstituted using 75 ml of sterile water.  How many ml will the nurse give per dose?

SF = 10,000,000  units

AU = mL

Equivalents:

1 mL = 250,000 units

4 doses

Equation:

The equation is 10 million units over 1 times 1 milliliter over 250,000 units. Cancel units. That leaves milliliters which is the answer unit. Solve the equation to get 40 milliliters. Divide by the 4 doses to get a final answer of 10 milliliters per dose.

 

  1. Client B has a prescription for 20 million units of penicillin G potassium IV daily in six divided doses.  The nurse uses 33 mL of sterile water to reconstitute a new bottle of  penicillin G potassium.   How many mL will the nurse give per dose?

SF = 20,000,000  units

AU = mL

Equivalents:

1 mL = 500,000 units (see label – amount of diluent has changed)

6 doses

Equation:

The equation is 20 million units over 1 times 1 milliliter over 500 thousand units. Cancel units. That leaves milliliters which is the answer unit. Solve the equation to get 40 milliliters. Divide by the 6 doses to get 6.66 which rounds to 6.7 milliliters per dose.

   

  1. Client C has a prescription for 30 million units of penicillin G potassium IV daily in six divided doses.  The nurse uses 75 mL of sterile water to reconstitute a new bottle of  penicillin G potassium.   How many mL will the nurse give per dose?

SF = 30,000,000  units

AU = mL

Equivalents:

1 mL = 250,000 units (see label – diluent has changed again)

6 doses

Equation for the dose in ml:

The equation is 30 million units over 1 times 1 milliliter over 250 thousand units. Cancel units. That leaves milliliters which is the answer unit. Solve the equation to get 120 milliliters. Divide by the 6 doses to get a final answer of 20 milliliters per dose.          

   

  1. The prescription for client C has changed to 25 million units of penicillin G potassium IV daily in four divided doses.  The nurse still has medication in the bottle of penicillin G potassium reconstituted with 75 ml of sterile water.  How many mL will the nurse give per dose?

SF = 25,000,000  units

AU = mL

Equivalents:

1 mL = 250,000 units

4 doses

Equation:

The equation is 25 million units over 1 times 1 milliliter over 250 thousand units. Cancel units. That leaves milliliters which is the answer unit. Solve the equation to get 100 milliliters. Divide by the 4 doses to get a final answer of 25 milliliters per dose.

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